In general, wireless communication systems are developed to support mobility of Mobile Stations (MSs). To ensure the mobility of MSs, a wireless channel is established between a Base Station (BS) and a MS in the wireless communication system. The established channel is used to perform voice and data communication. Therefore, while moving at a low velocity or a high velocity, the MS transmits and receives data through an occasionally changing wireless channel path and environment. Accordingly, the wireless communication system estimates a transmit (Tx) channel of the MS, and extracts data according to the result of estimation.
A method of estimating a channel of an MS may be used to determine a data transfer rate by estimating a velocity of the MS. In a known method of estimating the velocity of an MS, a BS estimates a Level Crossing Rate (LCR) by using Channel Quality Indicator (CQI) information periodically reported by the MS to the BS, and the velocity of the MS is estimated according to the estimated LCR. In this method, a filtered CQI curve is obtained by weight-averaging CQI values received using not only a current CQI value but also CQI values received through previous frames, and an LCR is measured by counting how many times the curve crosses an instantaneous CQI curve. For example, the greater the number of crossings, the faster the velocity of the MS. Further, the less the number of crossings, the slower the velocity of the MS.
When the velocity of the MS is estimated using the LCR, it is difficult to accurately estimate the velocity of the MS due to significant changes in the estimated LCR value. Therefore, only an approximate range of the velocity of the MS can be estimated using the LCR. If the velocity is greater than or equal to a specific velocity, it is difficult to know the approximate range when using the LCR. A graph obtained by estimating the velocity of the MS with respect to the LCR is shown in FIG. 6. In the graph of FIG. 6, the horizontal axis represents velocity, and the vertical axis represents an LCR count value. If LCR=25, it can be estimated that the velocity of the MS is 3 km/hr˜10 km/hr. If LCR=90, the fact that the velocity of the MS is greater than or equal to 20 km/hr is only information that can be obtained.
An LCR method is implemented with various elements, such as, a memory for storing instantaneous CQI values reported during hundreds of frames, a memory for storing weight-averaged CQI values during hundreds of frames, a counter for counting the number of crossings between a curve representing the instantaneous CQI values and a curve representing the weight-averaged CQI values, and a memory for storing data used to estimate a velocity by comparing LCRs. These elements need to be separately managed for all MSs connected to a BS, which leads to increased cost in system implementation. Further, when the velocity of the MS is estimated using LCR, the velocity is estimated not in a frame unit but in a unit of hundreds of frames. Therefore, it is difficult to estimate the velocity of the MS when the velocity of the MS instantaneously changes. Furthermore, the LCR value may increase again when a channel is similar to a Rician channel, and thus it is difficult to distinguish the Rician channel from a channel having a different velocity by using the LCR.
Accordingly, when the velocity of the MS is estimated using the conventional LCR method, it is difficult to estimate the velocity of the MS in an accurate and rapid manner, and large memory capacity is required.